1. Field of the Invention
This invention relates generally to an apparatus for high efficient distributed modular powertrain and optimum torque distribution control algorithm for electric vehicles.
2. Description of the Prior Art
In order to increase the driving range of an electric vehicle its powertrain must be highly efficient. For a state of the art electric powertrain the traction motor and its fixed gear transmission is designed to meet both performance and efficiency requirements. Whereas the performance criteria of a fully electric powered passenger car require high torque and power, the typical drive cycle of an electric vehicle is in the low torque and speed range. However, the state of the art traction motor has poor efficiency in this load range.
To gain higher efficiency of the powertrain in the typical drive cycle as well as for the homologation cycles, the traction motor's design must have rated power and torque output close to the load cycle. However, the performance criteria would be not fulfilled in this case, since they require higher rated torque and power.
One central electric motor used in an all electric vehicle has to be designed to cover the entire load range regarding acceleration, hill climbing and high speed requirements. However, a typical urban drive cycle as well as homologation cycles like UDDS, NEDC require the motor to be operated at low power and low torque profiles. Considering that the typical electric motor is designed to operate at its best efficiency near the rated power output, its best point of operation typically doesn't match with the homologation load paths. Designing the motor by setting up the best point of operation in the homologation cycle load path leads to lower torque output at high motor speed, which causes the motor to fail delivering enough torque in hill climbing or at high speed and high torque load scenarios.
A solution to this tradeoff is to use axle-wise distributed traction units designed for lower power output and to control them in a sufficient way. For low power operation only one axle is propelled. For high performance operation the second axle drive unit(s) are boosted in.
In case of different efficiency characteristics of front and rear powertrain units a drive control has been developed that operates the traction units in their optimum efficiency by optimized torque distribution between the drive units.